Summary: Senescence Is Induced in Individually Darkened
Arabidopsis Leaves, but Inhibited in Whole
Darkened Plants1
L. Michael Weaver* and Richard M. Amasino
The Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom
(L.M.W.); and Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison,
Wisconsin 53706 (R.M.A.)
It has long been known that leaf senescence can be induced in many plant species by detaching leaves and placing them in
the darkness. It recently has been shown that entire Arabidopsis plants placed in the darkness are not induced to senesce,
as judged by visible yellowing and certain molecular markers. Here, we show that when individual Arabidopsis leaves are
darkened, but not when entire plants are darkened, senescence is induced in the covered leaves. This induction of senescence
is highly localized. The phenomenon is leaf age dependent in that it occurs more rapidly and strongly in older leaves than
in younger ones, as is the case with many forms of induced senescence. Whole adult plants placed in darkness, in contrast,
show delayed senescence, although seedlings lacking primary leaves do not. These observations imply that the light status
of the entire plant affects the senescence of individual leaves. A model summarizing the results is presented.
Leaf senescence is an active process regulated by
exogenous and endogenous factors. An important
exogenous factor is light. The interplay between light
and senescence is complex, and many reports have
been published describing both its senescence-